In recent years, a waste solution exhausted from various industrial fields is being increased. As a waste solution, there are a factory waste solution, a beverage waste solution, and a body liquid waste solution. In particular, a liquid medical waste solution containing amniotic fluid or blood exhausted upon operation or delivery in hospitals is recovered in a waste solution canister, and is treated in a cleaning tank after burning-treatment or chemical treatment in order to prevent infectious diseases to medical workers or wasters.
However, in any case, since when a waste solution is treated in a liquid state, there is a possibility of secondary infection due to breakage of a waste solution canister or flying of a waste solution caused by occasional accidents, it is desired that a waste solution, in particular, a medical waste solution is treated after solidification (also referred to as gelling). That is, there is expected a method of treating a waste solution by placing a treating agent into a waste solution to solidify the waste solution into a gel.
Examples of a medical waste solution referred herein include blood and body fluid, a 0.90 mass % aqueous sodium chloride solution (physiological saline) mixed solution thereof, a Ringer's solution waste solution after washing of an affected part, a disinfecting ethanol waste solution, other disinfectant waste solution, an artificial dialysis waste solution, an organ containing body fluid such as blood isolated from a patient, and a pathological test waste solution.
In a waste solution treating agent for solidifying these medical waste solutions, several procedures for preventing reduction in water-absorbing performance of a water-absorbent resin due to an electrolyte contained in blood, body liquid or the like (e.g. patent documents 1 and 2 below) have been proposed. Patent document 1 describes a blend of an ionic water-absorbent resin and a nonionic water-absorbent resin. Patent document 2 describes a blend in which a substance which reduces an ionic strength of an electrolyte contained in a waste solution, for example, a chelating agent, an ion-exchange resin or ion-sensitive substance is incorporated in a water-absorbent resin.
However, in the procedure of patent document 1, although a nonionic water-absorbent resin hardly undergoes influence of an electrolyte, since an original water absorption rate is slow, in order to solidify a waste-liquid, a large amount of a solidifying time is necessary, or it is necessary to use a large amount of a water-absorbent resin. Further, a step of blending two kinds of water-absorbent resins becomes necessary, leading to a problem of non-uniform blending, or increase in a manufacturing cost.
Further, even when reduction in water-absorbing performance of a water-absorbent resin due to an electrolyte in such as patent documents 1 and 2 is prevented, there is a greater problem depending on the following waste liquid solidifying method (a shape of a canister and a method of placing a solidifying agent).
That is, as a method of solidifying a waste solution, various canister shapes (vertically oriented, laterally oriented etc.) and methods of placing a solidifying agent (simultaneous placement/divided placement into a waste liquid, pre-placement/post-placement into a solution) are proposed, but a waste solution is accommodated in a vertically oriented canister due to a problem of treating spaces in some cases.
However, when a water-absorbent resin is placed at once (post-placement in a waste solution) in order to solidify a waste solution, in particular, a medical waste solution stored in a vertically oriented waste solution canister, almost all water-absorbent resins are sunk to a canister bottom due to a density without floating, and solidification progresses towards an upper part of a waste solution. For this reason, a distribution of a water-absorbent resin after completion of solidification is such that the resin is distributed on a canister bottom at a high concentration, a part of the resin falls into a state like fisheyes in some cases, not all water-absorbent resin is used in some cases and, at an upper part of a canister, a water-absorbent resin concentration necessary for absorbing a waste solution becomes low, so the solidification is difficult to attain at an upper part of a waste solution canister.
As a result, as a method of solidifying a waste solution, when a waste solution is placed into a vertically oriented waste solution canister at once (post-placement into a waste solution), in order to solidify a whole waste solution, a large amount of a solidification time is necessary, or a large amount of a waste solution solidifying agent is necessary, in addition to a problem of non-uniform solidification between an upper part and a lower part in a vertically oriented canister.
Then, in order to shorten a time of solidifying a waste solution, a method of improving a water absorption rate by enhancing a surface area of a water-absorbent resin such as foaming and finely division of a water-absorbent resin, and a procedure of hydrophilizing a water-absorbent resin are proposed. However, under the present situation, even when a water absorption rate of a water-absorbent resin is improved, or the resin is hydrophilized, a sufficient waste solution solidifying rate is not obtained.
[Patent Document 1]    JP-A-119853/2002 (Kokai)
[Patent Document 2]    JP-A-169451/1999 (Kokai)